The elucidation of the enzymes involved in and the mechanism of adenovirus DNA replication is continuing. We have been able to isolate five protein fractions necessary for Ad-DNAx replication. These fractions are being characterized and a search for new ones is continuing. The initiation reaction of Ad-DNA replication in which an Ad-DNA protein complex if formed is being examined and the components essential for this are being isolated. Studies on the mechanism of control of the initiation of phi X RFI DNA replication are continuing. The nature of the ligase-type activity of the phi X gene A protein is being examined utilizing a plasmid which contains two gene A interaction sites as a template for in vitro DNA replication. The nature of lagging strand synthesis in these plasmids is being examined. The influence of various carcinogens on each of these DNA replication systems will be examined.